Drug withdrawal can be elicited as a conditioned response to environmental cues paired with drug use or withdrawal itself. Conditioned withdrawal is a powerful motivator of drug seeking in abstinent addicts just as acute withdrawal drives drug seeking in active drug users. For this reason it is of clinical interest to reduce or eliminate conditioned withdrawal states in recovering addicts. Extinction is a means of decreasing conditioned responses and involves exposure to a conditioned stimulus (CS) in the absence of the unconditioned stimulus (US) it signaled previously. Much has been learned about extinction of certain types of conditioned responses, such as conditioned fear elicited by a cue paired with an aversive event, but essentially nothing is known about extinction of conditioned opiate withdrawal. This application aims to begin a systematic examination of the mechanisms of extinction of conditioned opiate withdrawal using naloxone-induced conditioned place aversion (CPA) in morphine-dependent rats as a model system. Preliminary data indicate that CPA can be extinguished through repeated exposure to a previously withdrawal-paired environment in the absence of naloxone, and that CPA extinction can be facilitated by the NMDA receptor partial agonist D-cycloserine. The experiments described here will extend these findings in several ways. First, they will use basic pharmacological techniques to determine the role of NMDA receptor-dependent neuroplasticity within the basolateral amygdala (BLA) and infralimbic cortex (IL), two regions implicated heavily in extinction of conditioned fear, in CPA extinction. Second, they will use protein (Western) immunoblotting to investigate whether expression of NMDA receptor subunits within BLA and IL is modulated following CPA extinction. Third, they will examine whether viral vector-mediated elevations in NMDA receptor subunit expression with BLA and IL affect CPA extinction. The experiments are based on the hypothesis that BLA and IL are major players in CPA extinction and that NMDA receptor- dependent synaptic plasticity within BLA and IL is a critical mechanism underlying this form of learning. The hope is that with better understanding of the mechanisms of extinction of conditioned withdrawal will come better techniques for addressing the problem clinically, and ultimately improved outcomes for recovering addicts who are less vulnerable to relapse triggered by conditioned withdrawal. PUBLIC HEALTH RELEVANCE: Drug withdrawal can be elicited as a conditioned response to cues paired with drug use or withdrawal itself, contributing to relapse even after periods of abstinence. For this reason it is of clinical interest to reduce or eliminate conditioned withdrawal states in recovering addicts. The experiments described in this application will begin a systematic investigation of the neural mechanisms underlying one method of reducing conditioned withdrawal, called extinction, in which withdrawal-eliciting cues are presented repeatedly until the conditioned withdrawal response disappears.